OXYGEN DETECTION IN THIN SILICON DIOXIDE LAYERS BY LOW-ENERGY X-RAY-FLUORESCENCE SPECTROMETRY

Light element detection using low-energy (< 2 keV) x-ray fluorescence (XRF) is described. By tuning the energy of the incident x rays to sli ghtly above the absorption edge, the minimum detection limits for low- Z elements can be greatly improved over conventional XRF and signal-to -background is significantly better than that obtainable for electron- excited x-ray spectra using an energy-dispersive detector. In particul ar, the minimum detectable thickness of SiO2 is experimentally determi ned to be 0.36 angstrom (almost-equal-to 0.1 monolayer) film thickness for 1.85 kV anode voltage using a Mg anode with an Al window. Good si gnal linearity with film thickness is established by comparison with m easurements obtained on the same samples using ellipsometry and x-ray photoelectron spectroscopy.